Why don't you just get a METV from the start as its easy to get 8 months with a METV by arriving back in Thailand a day or so before the visa expires and you will get another 60 days. My advice would be don't bother with extensions unless you need to ,then if you want to extend your final 60 day stay for another 30 days giving you 9 months you should be ok.
There is also a rule a tourist can only stay in Thailand for a max of 180 days in a calendar year, your arrival day and leaving days are counted as well.
You can stay upto to a maximum of 60 days each time you enter each 60 days can be extended by 30 days if required or simply leave and you will get another 60 days each time you re-enter Thailand, if you time it correct you can get another 60 days if you re-enter a day before the 6 months is up and the extended it for 30 days giving a total of 9 months
You will be ok as you are obviously a genuine tourist ,it is people that are going out and back into Thailand many times only staying out for 1 day then returning, this is what they are clamping down on not genuine tourists
If you have not been doing boarder runs as in out and back in same day , and returned to your home country then there isn't a problem coming in on multiple visa exemptions
you must have a long term visa to get an account, tourist visas are no good for opening bank accounts also dtv's are classed as a tourist visa so no good to get a bank account.